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Gas drilling contaminates drinking water

Drilling for shale gas may pose a safety hazard if there are water wells nearby. But the controversial use of “fracking” does not appear to be a safety risk as regards water contamination.

Over the past decade, the use of fracking – a mining technique involving pumping water and chemicals underground to rupture rocks and bring trapped natural gas to the surface – has skyrocketed in Pennsylvania.

The state sits atop the Marcellus shale, a deposit estimated to harbour over 14 trillion cubic metres of natural gas. Residents have long expressed concerns that fracking could contaminate drinking water.

Now a study has shown that the real safety concern is the proximity of water wells to gas wells, and that fracking does not appear to increase the risk of water contamination.

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Rob Jackson of Duke University in Durham, North Carolina, and colleagues analysed water from 68 drinking wells in upstate New York, where fracking is banned, and Pennsylvania. They found that wells located within 1 kilometre of an active shale-gas drilling site contained 17 times as much methane on average as those further away.

The team was also able to confirm that the methane found in the drinking water came from deep within the Earth and was not produced at the surface by bacteria. The implication is that the contaminating gas came from the drilling sites.

Explosion hazard

While little is known about how this methane might affect health, its presence at elevated levels is an explosion hazard, says Jackson. Across the US, explosions in water wells have been linked to the presence of the gas in water. A 2008 report by the Ohio Department of Natural Resources found gas drilling to be at fault in one such explosion beneath a home.

Jackson says the methane is probably seeping out from cracks in gas well casings, so improving the way these are sealed should solve the problem.

Bryan Swistock, a water resources expert at Pennsylvania State University in University Park, says that the state has already introduced new standards for casing and sealing gas wells. “It would be interesting to continue this study [now the new standards are in place],” he says.

Journal reference&colon; Proceedings of the National Academy of Sciences, DOI&colon; 10.1073/pnas.1100682108